The above invention relates to a pallet for clamping a workpiece which is subjected to processing operations, e.g. machining operations.
It is generally known that, for machining in modern machining centers, the workpieces are arranged on a pallet and clamped in an accurate position on the pallet, one or more piston/cylinder units being used for the clamping operation. The piston/cylinder units used are actuated with the use of a pressurized fluid, e.g. hydraulic oil, and the forces applied are transmitted to clamping jaws which act on the workpiece to be processed and clamp the latter in position on the pallet.
After the operation for clamping the workpiece on the pallet has been carried out, the pallet is moved together with the workpiece along precision guides, which are arranged in parallel and are, for example, an integral part of a machining center in which milling attachments, drilling attachments and grinding attachments act on the workpiece.
In order to be able to actuate the piston/cylinder units which are arranged on the known pallet, each pallet has connections for the feed and the discharge of a hydraulic fluid. The fluid is delivered in flexible conduits in operative connection with a supply unit.
In the known devices of this type, the connection pieces arranged on the flexible tubes are provided with a thread in order to enable these connection pieces to be connected to conduits which are arranged on the pallet. The conduits on the pallet extend up to the piston/cylinder units of the pallet and serve to clamp the workpiece.
In order to be able to interrupt the flow of the hydraulic fluid which is fed to the conduits of the pallet, it is necessary to provide a specific ball valve for each inflow line and for each return line of the hydraulic fluid.
Therefore, in order to move a pallet together with a workpiece along the precision guide of a machine tool, it was necessary in the past to carry out the following steps:
The pallet had to be arranged together with the workpiece in a waiting position in order to close or open the clamping jaws which acted on the workpiece; a first connection piece had to be fitted in order to permit the feed of a pressurized hydraulic fluid to the piston/cylinder units; it was then necessary to check whether this connection piece was also properly connected to those conduits which led to the clamping devices; furthermore, a second connection piece with the associated conduits had to be fitted in order to permit a return of the hydraulic fluid from the pallet; after the fitting and the requisite checks had been carried out, it was necessary to open a ball valve in the feed lines and to actuate the pump of the supply unit; after the operation for clamping this workpiece had been carried out, a ball valve provided in the inflow line had to be closed and the delivery pump of the hydraulic supply unit had to be switched off; conduits which were provided for the inflow and the outflow of the hydraulic fluid then had to be connected, and it was then possible to feed the workpiece to the individual machining operations.
At the end of the machining operations on the workpiece, flexible conduits had to be connected again via connecting pieces in an unloading station for the workpiece, and a ball valve had to be operated in order to permit the return of the hydraulic fluid to the supply unit and in order to enable the machined workpiece to be unlocked.
The clamping and unlocking devices for pallets of the type described, as have been disclosed by the prior art, had various disadvantages.
Thus, first of all, it was necessary to pay great attention during the fitting of the feed tube and the discharge tube for the hydraulic fluid; the connection pieces for the feed and the return of the hydraulic fluid had to be subjected to a thorough inspection in order to avoid a pressure loss or an escape of hydraulic fluid from the piston/cylinder units of the clamping device during the feed movement of the pallet through the machining unit.
After the actuation of the clamping device, it was necessary to operate ball valves and the supply unit in order to open the clamping device.
During these actuating operations there was always the risk of incorrect manipulation, which could have very serious consequences, e.g. release of the workpiece during the transport movement of the pallet and during the machining of the workpiece.
The object of the above invention is to avoid the disadvantages of the prior art and to propose a novel pallet of the type mentioned at the beginning, in which the provision of ball valves in the conduits may be dispensed with, and to enable the hydraulic devices of the pallet to be fitted together with the conduits of the hydraulic supply unit without any risk of error, and furthermore to permit connection or release of the hose lines between pallet and supply unit with the greatest possible speed and safety.
These objects are achieved with a pallet for clamping a workpiece to be processed which is connected to a holding fixture which accommodates a quick-acting connection which is provided with conduits for the feed of a hydraulic fluid to a piston/cylinder unit of the pallet and with a quick-acting connection in combination with the return of the hydraulic fluid from the piston/cylinder units, in which case these first quick-acting connections can be connected to second quick-acting connections which are connected to a conduit for the feed of the hydraulic fluid and to a conduit for the return of the hydraulic fluid to a supply unit, the second connection pieces are arranged in a holding fixture which has an actuating lever for a connecting device, and the actuating lever is arranged on a disk which has an eccentric slot, and the eccentric slot can be connected to a guide pin which is fastened to the holding fixture for the first quick-acting connections.